1. Caltech Chemical Ionization Mass Spectrometer (CIMS) Measurements INTEX-NA Data Review John Crounse Alan Kwan Paul Wennberg

2. Instrument Block Diagram Not to scale

3. CIMS on DC-8

4. Measurements HNO 3 (0.5 s every 5 s) H 2 O 2 (0.5 s every 5 s) Peroxyacetic Acid (PAA, CH 3 C(O)OOH) –(0.5 s every 10 s) HCN (Flight #10 onwards) –(0.5 s every 10 s)

5. Calibration Online HNO 3 calibration from perm tube held at constant temp. Online H 2 O 2 calibration from urea- hydrogen peroxide held at constant temperature. Calibrations performed every hour.

6. Data Reduction Concentration = cts_signal_ion / cts_reagent_ion / F([H 2 O]) * cal_factor DLH-H 2 O was used for ambient water concentrations.

7. H 2 O 2 Measurements Compare well with URI HPLC/Fluorescence measurements There is an interference at high SO 2 and high H 2 O, this only affects a small fraction of measurements.

8. CIT/URI H 2 O 2 Comparison Median: 0.98 Mean: 1.10

9. Altitude Profile H 2 O 2

10. HNO 3 Measurements Compared with UNH well overall but with certain differences: Altitude trend, low altitude trend, biomass burning plumes.

11. HNO 3 Comparison

12. Fast HNO 3 and H 2 O 2 Measurements Interesting data within cloud, and around cloud/clear interfaces.

15. PAA Measurements Measured significant amounts of this molecule throughout mission, though it’s abundance was quite variable in space and time.

16. Significant concentrations observed. Mean:213 pptv Median: 188 pptv Falls off weakly with altitude. Highly variable in space and time.

17. Does PAA come from the thermal decomposition of PAN ?

18. PAA Lifetime? Atmospheric lifetime?? –Photolysis: 3-4 weeks  J = 5x10 -7 s -1 (Orlando, et. al., 2003) –Reaction rate with OH has NOT been measured!! Estimated to be 1-7x10 -12 from the measured rates of OH with HOOH, and CH 3 OOH. This gives lifetime of 2-12 days.

19. HCN Measurements Fair agreement with PANAK-HCN. CIT has high uncertainty at high H 2 O mixing ratios as product ion has a water dependent mass analog interference, as well as decreased sensitivity at high H 2 O. Fast HCN measurements may help understand complex air masses which may be a mixture of biomass burning and anthropogenic pollution.

20. HCN comparison versus altitude: Median: 0.88 Mean: 0.98

21. HCN altitude profile: Median: 279 pptv Mean: 302 pptv

22. Areas of interest Understanding atmospheric importance of PAA: sources, sinks, and lifetime. –Utilize model to help constrain these Measurements of HNO 3 and H 2 O 2 in clouds and around cloud/clear interfaces. Use of fast HCN measurements to help constrain ‘complicated’ air masses.